You would have a tough time shooting torpedoes in real life once they were in the water. They would be normally set to run at varying depths, a common setting being 8-10 feet. Bullets, even hi calibre or hi velocity ones do not penetrate very deep into water, due to waters natural resistance to compression. A common rifle calibre bullet, for example lose most of their velocity after only about 2 feet depth. Also, at shollower angles of firing most bullets will deflect off the surface of the water rather than penetrating.
Killing a torpedo would be almost impossible in real life becuase of these problems. The only way that it might possibly be done would be to detonate a shell near the torpedo, such as from a 5 inch gun. I suppose there is a possibility that the concussion from the explosion might detonate the torpedo early.
